Lactobacillus helveticus has been employed for producing fermented milk for a long time as a typical lactic acid bacteria starter for dairy milk products. Lactobacillus helveticus has high proteolytic activity, and particularly, its extracellular proteinase having high activity plays an important role in fermentation of animal milk. That is, the extracellular proteinase digests animal milk proteins to produce various peptide fragments. The produced peptides are further subjected to the action of peptidases to become peptides of lower molecular weight. It is known that a part of peptides produced in a medium due to the action of proteinase enzymes is taken into cells of the lactic acid bacteria and utilized as a nitrogen source. It has also been reported that some of the peptides produced in the medium have an inhibitory activity against angiotensin converting enzyme (ACE) which causes hypertension. (J. Dairy Sci. 78:777-783(1995)).
As peptides for inhibiting ACE activity and suppressing rise in blood pressure, various effective peptides have been reported, such as those derived from degradation products of milk proteins, soybean proteins or fish meat proteins. For example, Val-Pro-Pro and Ile-Pro-Pro (abbreviated hereinbelow as VPP and IPP, respectively. These peptides are collectively referred to hereinbelow as lactotripeptides) are known as peptides having ACE inhibitory activity present in a Lactobacillus helveticus—fermented milk. These lactotripeptides have been confirmed to have a strong hypotensive effect by experiments using spontaneously hypertensive rat (SHR) (J. Dairy Sci. 78:1253-1257(1995)).
However, the lactotripeptide-containing fermented milk produced by fermenting animal milk with conventional Lactobacillus helveticus strains can hardly be taken as it is, because it exhibits high acidity due to a large quantity of lactic acid generated as the fermentation progresses. Dilution of the fermented milk results in extreme decrease in the content of the lactotripeptides.
Thus, it is desired to produce fermented milk with higher content of the lactotripeptides compared to the content of the lactic acid generated in the fermented milk. With an addition of a small amount of such fermented milk to various foods and beverages, products having the function of the lactotripeptides could be prepared easily and provided to consumers in an agreeable form to take. However, none of known lactic acid bacteria strains produce the lactotripeptide with high efficiency.